Underground utility equipment enclosures include the so-called grade level vaults, splice boxes, pull boxes, and the like, for various applications requiring access to an underground service. These may include electrical, gas, water, telephone, fiber optics and cable TV installations, for example.
Grade level enclosures are commonly subjected to different kinds of structural loads during use. Generally speaking, prior art enclosures and their cover plates are made from reinforced concrete, fiberglass, or polymer concrete composite materials for added load strength, to withstand the compression forces during use.
Grade level enclosures, particularly those used for telecommunications equipment, are adapted to facilitate use with different types of internal equipment. They may include splice cases, fiber optic cables, electrical wires, and the like, supported in the enclosure by metal cable racks fastened to upper portions of the enclosure's inside walls.
Industry standards have been developed for conformance tests and requirements for the structural integrity of such grade level enclosures. One standard commonly used for underground enclosures is known as ANSI/SCTE 77-2010. This set of standards for underground enclosure integrity has Tier designations that relate to various load ratings to ensure proper performance for different types of underground enclosures. The objective of these standards is to ensure long product service life, minimized maintenance, and reduced product liability for those who design, develop, and market them.
In one example, the ANSI Tier designations relate to the normal design load×1000 lbs. For instance, Tier 15=15×1000 lbs=15,000 lbs. These ANSI Tier loadings have a corresponding test load which is 50% greater than the design load. For example, the test load for Tier 15=15,000 lbs×1.5=22,500 lbs. (Tier 15 [15,000 lb. design load, 22,500 lb. test load] is applicable to driveways, parking lots and off-road applications subject to occasional non-deliberate heavy vehicular traffic.)
The ANSI/SCTE 77-2010 performance specification includes a three-position structural test simulating wheels rolling over an enclosure where loads are imparted laterally and vertically onto the side wall of the enclosure and vertically onto its cover. The related structural integrity tests comprise:
(1). Position one—a lateral side wall test—a test of the area that must withstand soil forces as vehicles approach.
(2). Position two—a vertical side wall test—a test of load applied directly downward onto the vertical side wall.
(3). Position three—a cover test—a test showing how an enclosure responds to a load applied directly to the center of the cover.
The present invention provides an enhanced strength grade level utilities enclosure that can be made from lighter weight polymeric materials. In one embodiment, the enclosure's design provides enhanced structural loading capacity in excess of ANSI Tier 15 vertical side wall load and center cover vertical load requirements.
The ANSI Tier 15 test standards are one example of various industry test standards for grade level enclosures for which the present invention provides enhanced load capacities. Structural improvements, in particular, are demonstrated for enclosures' vertical side wall load capacities; and these improvements would result for different types of enclosures each having their own separate vertical side wall load capacity requirements.